1. Field of the Invention
The present invention relates to an integrated circuit transformer, and more particularly,to an integrated circuit transformer having two symmetrical conductive coils respectively disposed inside two insulating layers.
2. Description of the Prior Art
Owing to the dramatic development of semiconductors and the growing demand for wireless communications chips, conventional passive components such as transformers are usually integrated into a chip to meet the requirements of small size and low cost for a modern wireless communications chip.
In wireless communications integrated circuits, an integrated circuit transformer is capable of changing impedances for signal ends. To effectively reduce common mode interference, increasingly wireless communications integrated circuits adopt a differential approach to transform single-ended unbalanced signals into differential-ended balanced signals and vise versa. For example, a balance-to-unbalance (BALUN) transformer can transform single-ended unbalanced signals into differential-ended balanced signals.
Please refer to FIG. 1A to FIG. 1D. FIG. 1A is a schematic diagram of a BALUN integrated circuit transformer 10 according to the prior art. FIG. 1B and FIG. 1C are equivalent circuit diagrams of the transformer 10 shown in FIG. 1A. FIG. 1B shows an equivalent circuit diagram of the transformer 10 having two pairs of differential-ended signal ends. FIG. 1C shows an equivalent circuit diagram of the transformer 10 having one single-ended signal end and one pair of differential-ended signal ends. FIG. 1D corresponds to a cross section of the transformer 10 along a cross plane 11 shown in FIG. 1A.
The transformer 10 comprises a primary conductive coil 12 and a secondary conductive coil 14, both disposed above an insulating layer 16 (shown in FIG. 1D). The primary conductive coil 12 comprises a pair of differential-ended signal ends P+ and Pxe2x88x92. The secondary conductive coil 14 also comprises a pair of differential-ended signal ends S+ and Sxe2x88x92.
The primary conductive coil 12 and the secondary conductive coil 14 of the transformer 10 shown in FIG. 1A are interlaced with but not connected to each other. As the secondary conductive coil 14 crosses the primary conductive coil 12 or the primary conductive coil 12 and the secondary conductive coil 14 crosses themselves (as indicated by arrows shown in FIG. 1A), the primary conductive coil 12 or the secondary conductive coil 14 takes a bypass to another insulating layer first through a via plug and then returns to the original layer. Additionally, the primary conductive coil 12 and the secondary conductive coil 14 are symmetrical to a symmetry line 18. That is, both the primary conductive coil 12 and the secondary conductive coil 14 can be divided into two totally identical coils and these two pairs of identical coils are symmetrical to the symmetry line 18. Such a layout for the conductive coils of the transformer 10 can effectively reduce common mode interference. A first single-ended single end 17 of the transformer 10 is located at an intersection of an innermost coil of the primary conductive coil 12 and the symmetry line 18. Likewise, a second single-ended single end 19 of the transformer 10 is located at an intersection of an innermost coil of the secondary conductive coil 14 and the symmetry line 18. An impedance ratio for the pair of differential-ended signal ends P+ and Pxe2x88x92 and the pair of differential-ended signal ends S+ and Sxe2x88x92 is determined by the number of coils of the primary conductive coil 12 and that of the secondary conductive coil 14.
The above-described single-insulating-layer symmetrical transformer 10 is immune from the common mode interference. However, because the primary conductive coil 12 and the secondary conductive coil 14 are both disposed on the same insulating layer 16, the transformer 10 needs a large area to accommodate the primary conductive coil 12 and the secondary conductive coil 14.
Please refer to FIG. 2A to FIG. 2C. FIG. 2A is a schematic diagram of a dual-layer integrated circuit transformer 20 according to the prior art. FIG. 2B is an equivalent circuit diagram of the transformer 20. FIG. 2C corresponds to a cross section of the transformer 20 along a cross plane 21 shown in FIG. 2A. Note that the transformer 20 does not provide single-ended signals to differential-ended signals transformation. The transformer 20 also comprises a primary conductive coil 22 and a secondary conductive coil 24. The primary conductive coil 22 and the secondary conductive coil 24 respectively comprise a pair of differential-ended signal ends P+, Pxe2x88x92 and S+, Sxe2x88x92. An impedance ratio for the transformer 20is determined by the number of coils of the primary conductive coil 22 and that of the secondary conductive coil 24.
Contrary to the transformer 10 shown in FIG. 1A, the transformer 20 comprises two insulating layers. As shown in FIG. 2C, the primary conductive coil 22 is disposed inside a primary insulating layer 26 and the secondary conductive coil 24 is disposed inside a secondary insulating layer 28. Such a disposition of the primary conductive coil 22 and the secondary conductive coil 24 has the advantage to reduce the area of the integrated circuit transformer 20. However, because the primary conductive coil 22 and the secondary conductive coil 24 are lacking symmetry, the transformer 20 is vulnerable to common mode interference.
It is therefore a primary object of the claimed invention to provide a double-insulating-layer symmetrical integrated circuit transformer to solve the drawbacks of the prior art integrated circuit transformers.
According to the claimed invention, the multi-layer symmetrical integrated circuit transformer includes a first insulating layer, a first conductive segment formed inside the first insulating layer and disposed on a first side of a first line, and a second conductive segment formed inside the first insulating layer and disposed on a second side of the first line. The second conductive segment and the first conductive segment are symmetrical to the first line. A first end of the first conductive segment and a first end of the second conductive segment are connected to a point located on the first line. The transformer further includes a second insulating layer disposed on the first insulating layer, a third conductive segment formed inside the second insulating layer and disposed on a first side of a second line, and a fourth conductive segment formed inside the second insulating layer. The fourth conductive segment and the third conductive segment are symmetrical to the second line. A first end of the third conductive segment and a first end of the fourth conductive segment are connected to a point located on the second line.
The transformer further comprises a fifth conductive segment formed inside the first insulating layer and disposed on the first side of the first line, a sixth conductive segment formed inside the first insulating layer and disposed on the second side of the first line. The sixth conductive segment and the fifth conductive segment are symmetrical to the first line.
The transformer further includes a first connection conductive segment and a second connection conductive segment. A first end of the first connection conductive segment is connected to an end of the fifth conductive segment and a second end of the first connection conductive segment is connected to a second end of the second conductive segment. A first end of the second connection conductive segment is connected to an end of the sixth conductive segment and a second end of the second connection conductive segment is connected to a second end of the first conductive segment.
It is an advantage of the claimed invention that an integrated circuit transformer having a multi-layer configuration can reduce bulk and cost to designs.
It is another advantage of the claimed invention that an integrated circuit transformer having symmetrical conductive coils can be immune from common mode interference.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.